Numerical Study And Theoretical Design Of Novel Nozzle With Gaseous Film Cooling In DF/HF Laser

Currently, improving the operation reliability is one of the research topics in the field of high power continuous-wave(CW) DF/HF laser. And for the throat ablation problem existing in nozzle of the gain generator of current high-power CW DF/HF chemical lasers, the film cooling technique that has advantages in thermal and chemical protection is considered to protect the wall and throat of the nozzle.In this paper, the nozzle cooled by gas film whose flow rate is controlled by an orifice was modeled, meanwhile, the distribution of its flow field parameters was also simulated. Then we mainly analyze the influence of changes in flow rate and slit width of gas film on the flow field parameters of nozzle. The simulation results show that, to some extent, the existence of the gas film does protect the nozzle, and with the increasing of gas-film flow at the nozzle wall, the content of helium increases while the temperature drops, which enhances the protection effect. However, the gas-film flow rate should not be too large because of the dilution and cooling effect of helium film. It also should be noted that changes of the gas-film slit width did not bring big changes to the flow field so that we just need to design the slit width properly. The empirical formula of the main stream and the theoretical film throat width and the physical nozzle throat width was obtained by analyzing the interaction between main flow and gas film, and it can provide a reference for the throat parameter design of new-type nozzle, which will be the difficulty of this paper.The region that was considered was modeled and the temperature distribution and the water-cooling effect of the region was simulated. The results show that the water temperature in outlet is too high to get close to or even exceed the boiling point when the water flow rate is enough low. Eventually, a suitable water flow rate corresponding to the conditions of the model was proposed by simulations, which provides an important method and data reference for the design of relevant experiments.Finally, on the basis of experimental data and parameters of the previous test platform for a laser, the main structure parameters and gas supply flow rate of the combustion chamber injector, combustion chamber, nozzle, ignition, gas film channel were calculated according to the formulas and rules obtained from the simulation in this paper. Above all, the design of verification experiment for the cooling effect of gas film has been completed preliminarily.